Last.fm

So this week we're talking about "harnessing collective intelligence", meaning using a web application's users to enable it to develop and grow. Users can contribute in an explicit sense by directly adding or altering content, or implicitly by their day to day use of the application.
Last.fm makes strong use of this on multiple levels. Last.fm is an internet radio site that builds a profile of the music a user listens to via a lightweight plugin, whether through radio stations, portable devices or computers, and recommends new music based on the listening preferences of others. By simply listening to music with the plugin installed, users are contributing data to Last.fm's "scrobbled" database. The site automatically generates pages for new artists once a user has listened to them. Users are constantly contributing implicitly to the database and site. The site also tracks popularity of artists and songs by the amount of times they are listened to.
The site also makes use of explicit contributions by users in the form of tags, videos and events. Users can also personalise their pages with avatars and personal information, as well as being able to embed their "recently listened to" tracks into sites such as Facebook and blogs.
The thing that strikes me about Last.fm is that it encourages user participation by allowing users who are passionate about music to connect with others. While Last.fm offers the ability to connect with people with similar taste in music all over the world, as well as to discover new music through recommendations and communities, I think a lot of the drive for people who contribute explicitly is to tell everyone how much better my taste is than yours. The Shoutbox on the page for the Melvins, one of my favourite bands, is a long stream of abuse between the band's fans and people who hate their music, but somehow feel the need to tell fans that they have terrible taste.
Photo from Flickr.

Haiku

Thirty million-odd
Hipsters waiting to tell you
How bad your taste is.